*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

.rule{
    position: fixed;
    right: 0;
    top: 20px;
    background-color: skyblue;
    color: white;
    border-radius: 90px 0 0 90px;
    height: 90px;
    line-height: 90px;
    font-size: 30px;
    padding: 0 20px;
    border: none;
    outline: none;
}
.mask{
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0,0,0,0.5);
    display: none;
}
.a{
    position: fixed;
    left: 50%;
    top: 50%;
    width: 500px;
    background-color: chartreuse;
    border-radius: 5px;
    transform: translate(-50%,-50%);
    text-align: center;
    padding: 100px 0;
}

.a>button{
    width: 100px;
    height: 40px;
    background-color: aqua;
    color: white;
    font-size: 15px;

}